The present invention relates generally to downhole circulation subs. More particularly, this invention relates to the use of an electric motor to drive a downhole circulation sub.
Retrieval of oil and other hydrocarbons form below ground typically includes drilling a borehole, also known as a wellbore, in the Earth. As drilling technology has advanced, these boreholes may be drilled off of vertical, sometimes even sideways or horizontal. In this way, an operator can reach a formation that contains the desired substance. Thus, the terms xe2x80x9cupperxe2x80x9d and xe2x80x9clowerxe2x80x9d, or xe2x80x9cabovexe2x80x9d and xe2x80x9cbelowxe2x80x9d as used herein are made with respect to a position in the borehole, and may not necessarily reflect whether two elements are above or below each other in an absolute sense. FIG. 1 includes rock formation 100 surrounding a borehole 110. Borehole 100 is formed by the cutting action of drill bit 125 attached to rotating drill string 120. Drill string 120 also includes a circulating sub 170.
A variety of drill bits 125 are known, but a common feature is that each contains ports or nozzles on its face to direct drilling mud 130 (also known as drilling fluid) flowing through drill string 120. The drilling mud 130 exits the drill bit as shown by arrows 160. This mud not only cools the face of the drill bit, but also carries to the surface a substantial amount of shavings and cuttings 140 that result from the drilling action. These cuttings are carried up to the surface from downhole along an area between the drillstring and the borehole wall known as the annulus 150. At the surface, the drilling mud is then cleaned, filtered and recycled for repeated use.
One problem occurs when the ports or nozzles on the face of the drill bit 125 become blocked or otherwise impeded from spraying drilling mud out the face of the drill bit 160. This prevents or substantially slows the flow of mud to the surface, resulting in the rock cuttings falling to the bottom of the wellbore. It also results in a pressure build-up in the mud contained in the drill string. The increase in pressure can damage equipment uphole such as pumps. To minimize this problem, it is known to provide a circulating sub 170 that provides an alternate route 165 for drilling mud flow when the mud is unable to exit drill bit 160 properly.
Referring to FIG. 2, a known circulating sub 200 is called a ball-drop circulating sub. It includes a cylindrical valve sleeve 210 having holes or ports 220. At its lower end is a lip 230 that reduces the inner diameter of the cylindrical valve sleeve 210. The circulating sub housing surrounds valve sleeve 210 and also includes ports 225. Shoulder 260 is positioned for abutment against the lower portion of valve sleeve 210, as explained below. Between valve sleeve 210 and drill string 120 are o-rings 240-242 and a shear pin 250. Ball 270 is shown falling in mid-travel from the surface before lodging in area formed by lip 230.
During normal operation (i.e., when mud is properly flowing 160 through the drill bit 125), drilling, mud 130 flows through the center of circulating sub 200 as shown by arrows 280. However, upon a blockage in the flow of mud, a ball 270 is shot from the surface down to ball-drop circulating sub 200. Ball 270 lodges against lip 230, preventing the flow of mud 130 along flow path 280. Pressure built up in the mud column exerts itself against ball 270 and causes shear pin 250 to break. Valve sleeve 210 drops down until stopped by shoulder 260. This aligns ports or holes 220 and 225. Drilling mud 130 then escapes circulating sub 200 and follows mud path 165 (shown in FIG. 1) to the surface. This lifts the rock cuttings above the circulating sub 200 to the surface. However, the ball-drop circulating subs have a number of problems. For example, because the ball 270 originates at the surface, it can take up to thirty minutes from the time the mud flow stops through a drill bit to the time the circulating sub redirects the flow. In addition, this design is a one-time actuation and cannot be reset.
Other circulating subs having various problems, such as U.S. Pat. No. 5,465,787, are also presently known.
A preferred embodiment of the present invention features a downhole circulation sub having an electric motor associated with a valve poppet. The valve poppet moves from a first position to a second position in response to force from the electric motor, causing drilling fluid flowing through the circulation sub to switch its path of travel from a first route generally downwhole to a second route generally uphole. In its second position, the valve sleeve may engage a valve plug. Further, the valve poppet may be placed back in its first position by operation of the electric motor. The circulation sub is designed so that this movement of the valve sleeve from its first to its second position, and back again, may be carried out repeatedly.
Another aspect to the invention is a method of redirecting the flow of drilling fluid in a circulation sub. This aspect of the invention includes actuating an electric motor to apply force to a connected valve sleeve, moving the valve sleeve from a first position inside a housing to a second position by actuation of the electric motor, preventing by movement of the valve sleeve to the second position the flow of fluid past a lower end of the circulation sub, and directing by the movement of the valve sleeve to the second position the flow of fluid through ports positioned between the valve sleeve and an annulus. The first position is typically an upper position with respect to a wellbore, and the second position is a lower position.
Thus, the present invention comprises a combination of features and advantages which enable it to overcome various problems of prior devices. The various characteristics described above, as well as other features, will be readily apparent to those skilled in the art upon reading the following detailed description of the preferred embodiments of the invention, and by referring to the accompanying drawings.